This invention relates to oscillators comprising a distributed network resonator for microwave radiation. In particular the invention relates to MIC (microwave integrated circuit) oscillators that are frequency tunable and have temperature stability notwithstanding the temperature instability of their active elements. The invention also relates to a particular device taking advantage of the novel oscillator, namely an acceleration, pressure and displacement sensor that converts those physical parameters into electromagnetic mode modifications within the resonator component of the oscillator.
Temperature stable MIC oscillators are known in the prior art. In particular U.S. Pat. No. 4,565,979 to Fiedziuszko discloses a dielectric resonator for stabilizing a microwave oscillator. The resonator has lower and upper cylindrical dielectric elements that are linked by a magnetic mode of a microwave field. Mechanically, the cylindrical elements have their symmetry axes parallel but slightly offset. A dielectric tuning screw, having a coefficient of thermal expansion between those of the dielectric elements adjusts the separation between the elements. A drawback of the Fiedziuszko patent is the requirement that the two cylindrical elements stand one above the other thereby necessitating a relatively thick structure in a structure that otherwise is designed to be planar.
Other prior art has attempted to improve the temperature independence of the MIC circuits. In particular, U.S. Pat. No. 3,475,642 to Karp disclosed an array of high Q dielectric resonator elements such as TiO.sub.2 coupled together by their external magnetic fields for such purposes as an oscillator frequency control. The coupling is varied by adjusting the spacing of the array. Although the elements are cylindrical, the patent teaches that because of the substantial separation of the elements of the array, the coupling is independent of the shape and orientation of the individual elements. (Col. 2, line 68). Nevertheless, the patent teaches that thin disks should be used because it results in separation of the various resonant frequencies. (Col. 3, line 5). The disks making up the array are stacked like alternating slices of salami ("disk-like elements being positioned spaced from one another with their axes in alignment") and supported to be movable toward and away from each other to vary the pass band of the array.
U.S. Pat. No. 4,079,341 to Linnet al. discloses a dielectric resonator located near a semiconductor device, such as a microwave bipolar transistor or microwave field effect transistor, to stabilize a microwave oscillator circuit having the device as a component. The resonator provides a feedback path between the electrode terminals of the device. A dielectric spacer, located between the electrode terminals and the resonator, controls the coupling between the terminals. The dielectric resonator is shown as an integral component which is movable as a unit. The criticality of dimensions is recognized by disclosing that materials used must be compensated for thermal expansion.
U.S. Pat. No. 4,149,127 to Murakami et al. discloses a dielectric resonator stabilized oscillator in which the resonator forms a feedback element. The device uses micro-strip lines forming a feedback circuit coupled to the dielectric resonator.
U.S. Pat. No. 4,187,476 to Shinkawa et al. discloses a FET having a feedback path between gate and drain or source and a resonator connected to the gate. A temperature sensitive semiconductor steadies the oscillation frequency against ambient temperature fluctuation inherent in the use of the resonator.
U.S. Pat. No. 4,307,352 to Shinkawa et al. discloses an arrangement of a microwave oscillator having a micro-strip line with an FET and a high Q dielectric resonator. The coupling position of the dielectric resonator is selected to form a self-oscillation loop between the FET and the resonator causing oscillation at the resonant frequency of the dielectric resonator. The patent discloses the sensitivity of the resonant frequency to the distance between the dielectric resonator and the conductive substrate of the assembly, a distance that is temperature dependent. The patent discloses cutting away the surface above the grounding conductor and having the dielectric resonator sit directly on the conductor.
U.S. Pat. No. 4,331,940 to Uwano discloses a planar MIC (microwave integrated circuit) band rejection filter formed from a resonator coupled to a transmission line. The load impedance is adjusted by the position of the resonator. A capacitive susceptance stub conductor pattern on the dielectric substrate is connected to the transmission line near the coupling point of the resonator and gives improved temperature stability.
U.S. Pat. No. 4,333,062 to Uwano disclosed two strip line resonators in a planar MIC solid state oscillator. Low Q resonators are used which are incapable of pulling the oscillation frequency to their resonant frequency, but this is compensated by using chip capacitors with temperature compensating characteristics serially in the middle of the strip line resonators.
U.S. Pat. No. 4,357,582 to Ishihara et al. proposes a specific geometrical arrangement for a microwave oscillator in which a dielectric resonator is disposed within the angle formed between the gate transmission line and the drain transmission line of a FET disposed on a planar substrate.
U.S. Pat. No. 4,435,688 to Shinkawa et al. discloses a microwave oscillator formed from a micro-strip line, a dielectric resonator and an FET having a capacitive element between the source of the FET and another FET terminal. The object is to compensate for the temperature drift of the FET by providing a suitable capacitive reactance.
U.S. Pat. No. 4,445,097 to Godart et al. discloses another such oscillator in which the FET gate is connected one quarter wavelength from the end of a line coupled to a dielectric resonator and terminated by a discrete resistor in series with a half wavelength open circuit line.